The effects of organophilic rectorite (OREC) content and interfacial interaction on the nanoscale free volume, the crystallinity, and the heat distortion temperature (HDT) have been studied for nylon 6/layered nanocomposites by positron annihilation lifetime spectroscopy (PALS) and dynamic mechanical analysis (DMA) etc. Experimental results indicated that both HDT and crystallinity increase with filled OREC due to the nucleating or epitaxial effect of nanoparticles filled and interfacial interaction between the OREC and matrix. A continuous positron lifetime analysis program based on maximum entropy lifetime method (MELT) was used to obtain the free volume distribution, which revealed the existences of two long-lived lifetime components (t3 and t4) corresponding to two kinds of different free volumes. We introduced a new parameter A defined as A = At3/A (t3 + t4) and found a direct linearly relationship between the A and the crystallinity, which suggested that t3 is mainly attributed to ortho-positronium pick-off annihilation in the interstitial free volume of the crystalline region. Experimental results also found that the interfacial interaction has different effect on the free volume properties in the different temperature range, which can be explained by a model that describes the evolution of the interfacial interaction area with temperature. POLYM. ENG. SCI., 2012. (C) 2012 Society of Plastics Engineers